1. Field of Invention
The present invention relates generally to methods and apparatus for use in phosphatizing. More particularly, the present invention relates to methods and apparatus for phosphatizing objects with a closed loop pressure washer and phosphatizer system, or similar device, and recovering and recycling rinse solution to replenish evaporated phosphatizing solution.
2. Description of the Relevant Art
Contamination of the environment by man-made substances has been considered a serious problem for a long time. Recently, concern about contamination of earth, air, and groundwater by oil, toxic chemicals, and other hazardous wastes has expanded beyond large-scale industry to encompass the activities of many small businesses including automobile service stations, and many others. Both government regulations and social outcry have placed tremendous pressure on these businesses to avoid discharging hazardous wastes into the environment in the course of ordinary business activities.
Many businesses partake in activities which are likely to produce waste which may be harmful to the environment. For example, in an automobile service station, washing or steam-cleaning auto parts, e.g., an automobile engine, often causes engine oil, gasoline, and other chemicals to enter a storm drain system, or other waterways, thereby leading to the potential contamination of groundwater. In addition, those who service remotely located equipment generally have a need to wash the equipment without discharging hazardous waste into the environment. By way of example, persons who service roofmounted air conditioners that contain lubricating petrochemicals, trapped pollutants, or other chemicals are not permitted to wash the equipment in a manner that could cause chemicals to run off the roof and into the surrounding environment.
These environmental concerns also apply to phosphatizing metal objects which is a pre-treatment process of metal for powder coating or wet painting. More specifically, in this process, a low concentration of phosphate solution reacts with the iron in the composition to create an iron phosphate coating. Similar to iron oxidation, the phosphate binds up with the site to form a coating which prevents further oxidation. Thus, this surface oxidation or etching creates an acceptable porous surface for the powder coating to statically adhere to the metal, and an acceptable surface for wet painting. Subsequently, the powder is heat cured to bond the powder to the treated surface.
Phosphatizing is usually a commercial multi-stage procedure where the main process of phosphatizing is typically performed through a dipping bath or spraying application. Generally, phosphatizing is performed by large commercial establishments having relatively large and costly conveyor-type systems which move the metallic objects to be phosphatized systematically through each process stage. Depending upon the quality of the paint desired, more intermediate stages are added which increases the quality of the painting. In these costly conveyor-type assemblies, however, the primary stages prior to powdering usually include a cleaning process, a phosphatizing process, and a finishing rinse.
The cleaning stage is usually performed using a heated spray application of water to the surface of the object under high pressures of between about 500 psi to about 2500 psi, depending upon the metal composition. This washing procedure removes any loose particles, surface oils or the like which may adversely affect the formation of the iron phosphate coating on the metallic surface during the phosphatizing stage. In conveyor-type systems, such high pressure cleaning is usually applied by spraying the object through pressurized nozzles strategically located about the conveyor assembly in the cleaning station. Since these nozzles are usually fixed relative the conveyor assembly, cleansing coverage of the metallic object is often limited.
The next stage of the procedure is the phosphatizing step where the pressure cleaned objects are phosphatized using a primarily heated solution of 1% to 5% phosphoric acid solution. Chemical constituents of phosphate solution will vary from manufacturer to manufacturer.
In large conveyor-type systems, this stage is usually applied in a spray application to bath the object in the phosphate solution. Similar to the washing station, the phosphatizing station includes a plurality of strategically placed spray nozzles fixed about the station. Therefore, coverage of the phosphate solution on the object is limited in the same manner as in the washing bath. To some extent, this limits the coverage dimensions of iron phosphate coating which is dependent upon several factors including the phosphate concentration, the coverage of the spray application and the amount of reaction time.
The final stage of the phosphatizing process is the finishing rinse stage where de-ionized water is preferably employed to rinse the phosphoric acid solution from the object to inhibit further phosphatizing of the object surface. In effect, this finishing rinse procedure halts the reaction by removing the phosphatizing reagent from the surface of the coated object. It is important, however, to rinse the phosphatized object from a source of continuous clean de-ionized water to assure proper rinsing of the object. De-ionized water even slightly contaminated with phosphoric acid will not properly halt further reaction of the phosphatizing process. Thus, this rinsing solution must not be reused, and is discarded after use.
Due to environmental restrictions, this contaminated refuse must be treated before being discarded into the environment. Thus, hazardous waste disposal units must be contracted, or other costly disposal processes are applied such as the application of phosphate neutralizers to the waste before being discarded. In other instances, evaporators or the like must be employed to evaporate the water, leaving hazardous solid phosphates wastes for removal.
While these large conveyor-type phosphatizing systems are adequate for large commercial establishments with large productions, they are not practical for most mid-size or smaller establishments with substantially less resources and production capabilities. For one, these systems are relatively costly and require relatively large areas of manufacture space. Further, the maintenance costs of the systems is substantial. For example, the recommended use of de-ionized water for the washing, phosphatizing and rinsing stage collectively results in substantial production costs. Due to the volume of de-ionized solutions employed in each stage, water de-ionizing units to de-ionize tap water are employed as a continuous source of de-ionized water. However, this process itself is time consuming and costly to maintain. The Resin beds necessary to de-ionize the water are expensive and are easily contaminated. Thus, replacement is very frequent.
Thus, many phosphatizing units attempt to conserve the de-ionized water or even eliminate the use of de-ionized water. Regular tap water may be utilized to replace the costly de-ionized water in one of or all of the cleaning, phosphatizing and finishing rinse stages. This replacement, however, is often not recommended since the amount of dissolved solids/contaminants in the tap water vary depending upon the water source. Moreover, during the evaporation/replenishing cycles of tap water in phosphate solution, the build-up of dissolved solids/contaminants in the phosphate solution adversely affects the cleaning process. Thus, it is preferred to employ de-ionized water in both the cleaning, the phosphatizing and the finishing rinse procedures to reduce the number of dissolved solids/contaminants in the phosphate solution.
In other phosphatizing procedures, the rinse stage may be eliminated altogether. This technique is problematic, however, since it is then difficult to control the depth of the iron phosphate coating. Accordingly, while these cost savings applications reduce production costs, the quality of the phosphatizing is jeopardized in most instances.
One promising application is to combine the cleaning spray stage and the phosphatizing stage into one cleaning/phosphatizing stage. The primary problem with this application, however, is that the relatively high pressure of the spray application to clean the object is also too high to retain the build up of the iron phosphate coating. Thus, the coating is continuously blasted off the surface. The distribution of the iron phosphate coating on the object, consequently, tends to be more uneven.
Another problem associated with this approach is that the source of heated solution of phosphoric acid must be constantly monitored and periodically replenished. Depending upon the chemical manufacturers specifications of the phosphoric acid solution, the recommended operating temperature is usually in the range of about 120.degree. F. to about 160.degree. F. Thus, the evaporation rate is relatively high which ultimately results in a substantial loss of the water in the phosphatizing solution.